Developer Anonymous D who also made Console Grab has released SCS (S)ide s(C)rolling (S)hooter v1.0. It is a short but extremely fun side-scroller for the PSP. Note that this game was coded in Lua so you'll need a Lua Player to run it.

Like Gradius and other classic 8-bit shooters, this game scrolls from the left to right as you try to keep your ship alive. To kill the opposing ships, you have the option of blasting them with your gun or ramming them with your shields. If you ram them though, be advised that it takes away 25% of the shield strength. Don't worry though since it will slowly recharge once you've used it up.

All in all, this was a very solid effort from Anonymous D. Download the program and try it out. Like most homebrews, be sure to go over the readme document to avoid any potential mishaps that might damage your PSP.